It's also the main storage on the Wii, DSi, 3DS, (maybe Wii U, but it also had USB storage. I guess the Wii did too.) and Switch. An SD card reader lets you bac

It's also the main storage on the Wii, DSi, 3DS, (maybe Wii U, but it also had USB storage. I guess the Wii did too.) and Switch. An SD card reader lets you back up your game saves or install homebrew. More recently there's the PinePhone as well. It's not just expandable storage, you can boot off the SD and have all your OS and files there. I would say I definitely use SD cards more than flash drives now.